A method of transmitting message data via a server such as a mail server connected to a communication network is commonly used as a method of electronically transmitting a message through a communication network. An example of such technology is an e-mail system described in Japanese Patent Application Laid-Open No. 2000-305874. This e-mail system is configured to extract address information from a mail file, to convert the address information into a mail address, and to request a mail server to transmit a mail message.